1. Field of the Invention
The present invention relates to an apparatus for providing processing such as dewatering and drying of workpieces such as washed semiconductor wafers, for example, while spinning the workpieces in a chamber defining a clean environment.
2. Description of the Related Art
In manufacturing processes for making semiconductor devices and liquid crystal displays, sometimes there is a need to quickly dry disk-shaped workpieces or wafers which have been subjected to rigorous washing steps. Some of such apparatuses are based on drying the wafer by spinning off the liquid by centrifugal force in a chamber of so-called spin drying apparatus. There are two types of spin drying apparatuses: a vertical type with a vertical spinning axis with the advantage of a small installation space, and a horizontal type with a horizontal spinning axis with the advantage of convenient vertical loading of wafers.
Both type of spin drying apparatuses share a common structural feature that a workpiece is held in a rotating wafer holder, having a rotation shaft extending along the rotational axis of the holder inside a chamber. In a widely used design for supporting the wafer holder, the rotation shaft is rotatably supported through a contact-type bearing and is united to a drive shaft of a drive device by mechanical coupling.
However, such contact-type bearing mechanisms for the rotation shaft are vulnerable to wear and generation of wear debris, presenting a problem of contamination of the wafers which had been subjected to careful cleaning. Another problem is that the service life of the bearing device is shortened by frictional wear, resulting in a lower operation efficiency due to frequent requirements for maintenance. The working environment is also degrade by noise generated by the operation of high-speed spin dryer.